Methods for producing vinyl ethers



Johann Sixt;

States, Patent P r 2,984,688 m nons non pnonuciNo VINYL Muhieh;G'ermanypassignor to' Wacker- ChemievG.mLb.H., Munich, Germany, a Germanfirm nojnrawin fliilddFeb, 1'6, 1959,5er1No. 793,257 Claims priority,applic ation Germany Nov. 18, 195 5 p s Claims c 260-614) The resentinvention relates to an improved process for the production of vinylethers;

This. application'wis a continuation-in-part: of mycopending'application Serial No. 622,781, filed November 19,; 1 9S6"andwnow abandoned.

Vinyl ethers have been obtained by the reaction of In the abovereaction; both R and R alkyl groups. 8 l

omymoderateyiem are obtained in accordance with the above process, andthere is a marked difference observed between molar yield, of thedesiredgvinyl ether and the molar yield of the organic acid formed asthe byproduct of the reaction. Theoretically, of course, both productsshould be obtained in equimolecular yields. When, for example, vinylacetate is the vinyl ester employed in the reaction, an accuratemeasurement of each of these variables, namely, the amount of alcoholreacted on the one hand, and the amount of acetic acid formed on theother hand, and also the amount of vinyl acetate reacted, give a fairlyaccurate indication of the precise course of the reaction so far asconversion and yield are concerned.

It is to be noted, however, that in this reaction when carried out inthe usual fashion the conversion based on the amount of organic acidformed is always considerably higher than that based upon the vinylacetate reacted. The discrepancy is particularly evident in theproduction of vinyl ethyl ether where, for example, when 1 mol ofethanol is reacted with an excess of vinyl acetate, 6 mols for example,in spite of the fact that 0.6 mol and more of acetic acid are formedonly 4 grams of vinyl ethyl ether are obtained, which corresponds to ayield of only 0.055 mol. Calculated as percentage yields, this amountsonly to a conversion of but 5% of the alcohol employed with a molpercent yield of vinyl ether based upon the acetic acid formed of0.055206 or 9%. If along with the 0.6 mol of acetic acid 0.6 mol ofvinyl ethyl ether had been formed, it would have amounted to a yield of43.2 grams.

It has now been found that vinyl ethers may be obtained in high yieldsin accordance with the above reaction and with a relatively high molpercent ratio of vinyl ether being formed compared to the acid byproductif the vinyl ester is reacted with an aliphatic alcohol having not morethan six carbon atoms in the presence of not more than 0.5% of a strongacid and a catalyst comprising mercuric oxide or the mercuric salt of aweak are lower aliphatic acid at atemperature not higher 15 C. the vinylether is distilled, off from the' reaction mixture during T theformation of such undesirable byproducts as the reaction as it isformed; Preferably a reaction tem- Patented May 16', 1961 3 employedtogether with subatmospheric pressures in the reaction system to aiddistillation; Since the vinyl ether produced is immediately distilledoff as it is formed-, the period during which the vinyl ether is subjectto contact with the reaction mixture is as short as possible and sidereactions reducing the yield are greatly minimized, with and acetoxyacetals being heldtd a minimum. 1

As indicated, the distillation of the vinyl ether formed is greatlyaidedby maintaining the system under a sub atmospheric pressure and thedistillation can be further accelerated by the introduction of an inertgas into the 3 amounts of the desired vinyl ether. The residue may be isystem during distillation, for example, nitrogen so that the systemis'swept b'y the gas strearri'. Sulfuric acid is preferably employed "asthe strong acid and from 0.05 to" Oil percent byweight of the reactionmixture is adesalt may vary between widelimits'; usually 0.5 percent ofthe reaction mixture is suflicient.

thereaction' is completed the residue comprises the excess of unreactedvinyl ester, the aliphatic acid formed, 8

qu'atel Theadmixture of mercury oxide or of amercury 3 i.e. acetic acidin the case of vinyl acetate, and the catalyst. By adding furtherquantities of alcohol the reaction can be continued with the formationof further worked up in the usual fashion the addition of sodium acetatefollowed by distillation. The process described may also be carried outin a continuous manner by providingacontinuous supply of the reactantsto thereactor' I in the" preper maieeuiar' rano-ana ceminuousiydistilling off the vinylether" f'cirrned whilecontinuously removing Fthe unreacted residue, working it up and recycling the vinyl ester backto the system.

In order further to illustrate the present invention the followingexamples are given:

Example 1 Into a vessel provided with a stirrer, a connectingfractionating column and a dephlegmator there is introduced a reactionmixture consisting of 340 grams of vinyl acetate, 92 grams of ethylalcohol, 3 grams of mercury acetate and 0.05 gram of sulfuric acidcooled to a temperature of 15 C. The mixture is stirred and, as thereaction commences, distillation of the ethyl vinyl ether formed iscarried out immediately with the system at a pressure of 18 mm. ofmercury. The distillate is collected in a low temperature receiver. Theboiling point in the reactor gradually rises to -6 C. After 3 /2 hours128 grams of pure ethyl vinyl ether are collected and 112 grams ofacetic acid remain in the reaction vessel, as determined by an alkalinetitration. This corresponds to a conversion of 89% calculated upon theethyl alcohol consumed with a mol percent yield of ethyl vinyl ether,calculated upon the acetic acid formed, of 95.5%.

Example 2 Into a reaction vessel of the type described in Example 1 isintroduced a mixture of 500 grams of vinyl acetate, 32 grams of methylalcohol, 4 grams of mercuric acetate and 0.06 gram of concentratedsulfuric acid and the mixture is stirred for a short time at -15 C.Stirring is then continued and distillation of the methyl vinyl etherformed is effected under a pressure of 35 mm. of mercury. When the rateat which the reaction product is distilled over slackens somewhat, anadditional amount of 64 grams of methyl alcohol is slowly added to therem," 1 r. "s

action mixture without halting the distillation or breaking the vacuumwithin the vessel. During the courses of the reaction 159 grams ofmethyl vinyl ether are distilled over and 171 grams of acetic acidremain in the rsi'dueias det'e'rminedby titration. This amounts 'toiaryield or '91-%-calculated" upon the methyl alcohol con'-' sumedwith amolpercent yield of methyl vinyl ether:

based uponthe acetic acid formed of 9.6%.

Example 3- Vinylacetate isreacted methyl alcohol to form methyl vinylether. as described in Example 2. The apparatusemployed for carrying outthe reaction comprisesv a: packed, distilling column provided withsuitable heating means ,at-thebase, with;a. dephlegmator andwith asuit-yr able coolingjacketuin QrderLto-maintain any desired. low:

temperaturelwithinvthecolumn; in carrying out the reaction a vinyl:acetate mixture c'ontaining ,0.8%. by weight' of mercuric acetate and0.012% byweight of concentrated sulfuric; acid, and cooled, to a;temperature of l5C.,

is; fed to. the top of the column together with methyl alcoholin theratio ofpl6 parts byweight of vinyl acetate to each part by weight ofmethyl alcohol. The packed col-f umn:employed as the reactor ismaintained at 20 C.

by circulatinga cooling medium through thecooling jack-- et .andtheentire system is maintained under apressure of 35 mm. of mercury bymaens ,of avacuum pump. Vinyl methyl ether is formed as :the reactionproduct and is distilled ofl continuously at the head of the column at atemperature of about 15 C., A mixture of'acetic acid and the; excessvinyl acetate employed is obtained at the base of the column. Theconversion achieved amounts to'88% ,based upon themethyl alcoholconsumed and the yield of methyl vinyl ether on a mol percent basis,calculated upon the acetic acidformed, is 95%.

, 7 Example, 4

. Into a reaction vessel ofthe type described in Example l-is introduceda mixture of 75 grams of vinyl propionate, 64. grams of methyl alcohol,3 grams of mercuric acetate and 0.04 gram of concentrated sulfuric acid.The reaction mixture is stirred at a temperature of 15' C. 'and,

.. as thereaction commences the methyl vinyl ether :formed is distilledofi while maintaining the system under a pressure of 35 mm. of mercuryThe distillate is collected in a low temperature receiver and, after twohours, 90 grams of methyl vinyl ether are obtained which is equivalentto a yield of 85 molpercent based upon the amount of propionic acidformed.

:1; lation of the reaction prmluctoasit'is,tormed.;.-.;

Similarly, by employing propyl alc'oh'ol, bu tyl"alcohol or allylalcohol the corresponding prop yl -vinylgether; butyl vinyl ether or'allyl vinyl ether are. .formed-rtrawhen producing the highervinylethers itris preferred to employ lower pressures, as brought out,to'carry out the istil- Iclaim:

1.. In a process for the production of a vinyl ether which comprisesreacting vinyl acetate with a lower aliphatic alcohol having less thansix carbon atoms in the I presence of mercuricacetate. and less than:03% gofi'siilfuric acid based on the weight of the IeactaDts' thestepwhich comprises distilling 'ofi theivinyl etherras 'it is' for-med whilemaintaining the reaction mixture at .a temperature; of C. to C. andunder a pressure no higher than 35mm. of mercury; A v

2.1; Process. in accordance with alcoholis methanol.

3. Process in accordance cohol is ethanol.

tiara-"111i which the 1 5 can; 1 in which. the 251 Q References Cited inthe file of thislpatent- (1947), pages -186;

1. IN A PROCESS FOR THE PRODUCTION OF A VINYL ETHER WHICH COMPRISESREACTING VINYL ACETATE WITH A LOWER ALIPHATIC ALCOHOL HAVING LESS THANSIX CARBON ATOMS IN THE PRESENCE OF MERCURIC ACETATE AND LESS THAN 0.03%OF SULFURIC ACID BASED ON THE WEIGHT OF THE REACTANTS, THE STEP WHICHCOMPRISES DISTILLING OFF THE VINYL ETHER AS IT IS FORMED WHILEMAINTAINING THE REACTION MIXTURE AT A TEMPERATURE OF -5*C. TO -15*C. ANDUNDER A PRESSURE NO HIGHER THAN 35 MM. OF MERCURY.